1. Field of the Invention
The present invention relates to a microwave detector capable of detecting reverse detectors which are used to detect the presence of microwave detectors which emit an alarm upon detecting the microwave frequencies emitted by speed measurement devices.
2. Description of the Prior Art
Microwave detectors which generate an alarm upon detecting microwaves having the specific microwave frequencies emitted by radar type speed measurement devices are known in the prior art. Omitting a detailed description of the circuit construction, such microwave detectors generally operate by means of an antenna which picks up microwaves arriving from outside and a super-heterodyne type receiver circuit which receives microwave signals. Further, by sweeping the output frequency of a local oscillator in the related receiver circuit, such microwave detectors are able to ensure that the reception band width includes the microwave frequency of the detection target. Further, the local oscillator repeatedly carries out only a single sweep of the frequencies within the reception band width for each operation time period.
At this time, if a microwave frequency within the reception band width is present, the receiver circuit outputs two peaks P within a prescribed time interval t. In this way, because the microwave frequency of the detection target is fixed for the time interval t, the presence or absence of a microwave signal from the detection target can be determined by whether or not a pair of peaks P are present within the time interval t.
On the other hand, microwaves having prescribed frequencies leak out from the local oscillator provided in the microwave detector. Thus, by detecting such microwave frequencies leaking out from the related local oscillator, it is possible to construct reverse detectors to detect the presence of a microwave detector.
In this connection, because such reverse detectors also detect prescribed microwave frequencies, their basic detection principle is the same as that used by microwave detectors for detecting radar type speed measurement devices, and therefore such reverse detectors also include an internal local oscillator. Accordingly, microwaves having prescribed frequencies also leak out from the local oscillator of such reverse detectors.
Thus, by detecting the microwaves that leak out from the local oscillator of such reverse detectors, it becomes possible to detect reverse detectors. Further, as will be described below, because there is a different wave generation state for the microwave leaking from the microwave detector, the microwave leaking from the reverse detector and the microwave outputted from the radar type speed measurement device, it is possible to discriminate the signal generation source based on such differences.
Accordingly, in the example case where a reverse detector is detected, it is possible to suspend operations of the microwave detector for a prescribed period of time in order to suppress the generation of microwaves leaking out from the local oscillator housed internally in the microwave detector. In this way, it is possible to prevent the microwave detector from being detected by a reverse detection process. However, this method is not preferred because the essential process of detecting radar type speed measurement devices is temporarily suspended when the operations of the microwave detector are suspended for such prescribed period of time.